It is often necessary or desirable to determine the location of a medical probe relative to a location of interest within three-dimensional space. In many procedures, such as interventional cardiac electrophysiology therapy, it is important for the physician to know the location of a probe, such as a catheter (especially, a therapeutic catheter), relative to the patient's internal anatomy. During these procedures, a physician, e.g., steers an electrophysiology (EP) mapping catheter through a main vein or artery into the interior region of the heart that is to be treated. The physician then determines the source of the cardiac rhythm disturbance (i.e., the targeted cardiac tissue) by placing mapping elements carried by the catheter into contact with the heart tissue, and operating the mapping catheter to generate an EP map of the interior region of the heart. Having identified the targeted cardiac tissue, the physician then steers an ablation catheter (which may or may not be the same catheter as the mapping catheter above) into the heart and places an ablating element carried by the catheter tip near the targeted cardiac tissue, and directs energy from the ablating element to ablate the tissue and form a lesion, thereby treating the cardiac disturbance.
To facilitate the navigation of medical devices, such as mapping/ablation catheters, within the patient's body, various types of three-dimensional medical tracking systems (e.g., the Realtime Position Management™ (RPM) tracking system, marketed by Boston Scientific Corporation and described in U.S. Pat. No. 6,216,027 and U.S. patent application Ser. No. 09/128,304, entitled “A Dynamically Alterable Three-Dimensional Graphical Model of a Body Region,” and the CARTO EP Medical system, marketed by Biosense Webster and described in U.S. Pat. No. 5,391,199) have been developed, or at least conceived. In these medical systems, the position of the catheter can be determined within a three-dimensional coordinate system. Based on this positional information, a three-dimensional computer-generated representation of a body tissue (e.g., a heart chamber), along with a graphical representation of the catheter or a portion thereof, can be generated and displayed. In the case where a mapping catheter is tracked, electrical activity information can be acquired by the catheter and superimposed over the graphical representation of the tissue in the form of an electrical activity map.
To some extent, real-time three-dimensional tracking systems, such as the RPM and CARTO systems, have reduced the usage of real-time imaging modalities, such as fluoroscopy, during operative procedures. This is because the use of fluoroscopy in locating catheters is somewhat limited in that the physician is only able to visualize the catheter and surrounding tissues in two dimensions. In addition, fluoroscopy does not image soft tissues, making it difficult for the physician to visualize features of the anatomy as a reference for the navigation. Thus, fluoroscopy is sub-optimal for the purpose of navigating a catheter in three-dimensional space, e.g., within the heart. The use of fluoroscopy is also limited in that it poses the danger of exposing the patient and laboratory personnel to harmful doses of radiation.
Despite its limitations, the use of fluoroscopy is still used to generate real-time images of the relevant portions of patients' bodies during various medical procedures or portions thereof. For example, during medical procedures, such as angiography or angioplasty, fluoroscopy is often used to track catheters through the patient's vasculature to the targeted region, e.g., within a selected coronary vessel or chamber of the heart. In the case of interventional cardiac electrophysiology therapy, fluoroscopy can even be used in conjunction with real-time three-dimensional tracking systems, such as the RPM or CARTO systems. In particular, fluoroscopy may be used during the catheterization process (presumably before a graphical representation of the heart is even generated) to ensure that the catheter is introduced through the proper vessels and into the desired chamber of the heart, as well as to confirm proper placement of the catheter adjacent the intended anatomical structure within the heart. Also, because fluoroscopic images are capable of capturing dynamic conditions in real-time, fluoroscopy can also be used to confirm stability of the catheter within the heart, which is especially important during a tissue ablation procedure.
In any event, when an imaging modality, such as fluoroscopy is utilized, the operator (e.g., a physician, nurse, or technician) is typically required to manipulate the imaging system (or the position of the patient's body relative to the imaging system) in order to “aim” the imaging energy at the portion of the patient's body of which the image is desired at any given point in time. For example, in order to acquire the desired fluoroscopic images during a cardiac catheterization procedure, the operator must manipulate the position of the fluoroscope (which typically comprises a C-arm on which the x-ray source and detection components are mounted) relative to the patient (e.g., by moving the fluoroscope and/or moving the table on which the patient lies), such that the most relevant portion of the patient's body is imaged at any given time. For example, as the catheter is moved within the patient's vasculature, it is frequently necessary to periodically adjust the position of the fluoroscope relative to the patient, so that the catheter remains within the field of view of the fluoroscope. Furthermore, it may be necessary for the operator to adjust the orientation of the fluoroscope relative to the patient, such that the fluoroscopic image is generated from a particular point of view. For example, during a catheterization procedure, a physician may desire a fluoroscopic view that is perpendicular to the axis of a blood vessel to facilitate accurate measurement of the length of a vascular lesion or stenosis.
Unfortunately, manual adjustment of the position of an imaging system relative to the patient can be time consuming, difficult, labor intensive, imprecise, and inconvenient. Furthermore, because it may be necessary to visualize a real-time image to determine how to properly adjust the position of the imaging system, this manual adjustment process can lead to prolonged operation of the imaging system. This, in turn, may lead to increased radiation exposure (in the case of fluoroscopy) to the patient and/or medical personnel and may lead to premature failure or degradation of the imaging system due to extended operational time (i.e., components may wear out sooner). Manual adjustment may also not allow the degree of positional accuracy that may be desired. Lastly, because of the radiation danger associated with fluoroscopy, it is desirable to operate the fluoroscope only when it is needed. However, because it is often difficult to predict when fluoroscopic images of the relevant region should be generated, e.g., when a catheter becomes unstable, the fluoroscope may not always be operated when it is most needed.
There thus remains a need for an improved system and method for manipulating an imaging system, such as a fluoroscope, in a manner that facilitates imaging of only the relevant regions of a patient's body at the relevant times.